Calibrating tracking systems to remove position-dependent bias

• US 20080202200A1
• Filed: 02/22/2007
• Published: 08/28/2008
• Est. Priority Date: 02/22/2007
• Status: Active Grant

• Current Assignee: Accuray Incorporated
• Original Assignee: Accuray Incorporated
• Inventors: West, Jay B.
• Granted Patent: US 8,417,318 B2
• Time in Patent Office: Days
• US Class Current: 73/1.79
• CPC Class Codes: A61B 2034/2055 Optical tracking systems
• CPC Class Codes: A61B 2034/256 having a database of accessory information, e.g. including context sensitive help or scientific articles
• CPC Class Codes: A61B 2090/376 using X-rays, e.g. fluoroscopy
• CPC Class Codes: A61B 34/20 Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
• CPC Class Codes: A61B 5/1127 using markers
• CPC Class Codes: A61B 6/12 Arrangements for detecting or locating foreign bodies
• CPC Class Codes: A61B 6/583 using calibration phantoms
• CPC Class Codes: A61B 90/36 Image-producing devices or illumination devices not otherwise provided for
• CPC Class Codes: A61N 2005/1059 using cameras imaging the patient
• CPC Class Codes: A61N 2005/1062 using virtual X-ray images, e.g. digitally reconstructed radiographs [DRR]
• CPC Class Codes: A61N 5/1049 for verifying the position of the patient with respect to the radiation beam
• CPC Class Codes: A61N 5/1067 in real time, i.e. during treatment

Abstract

A method for removing position-dependent bias from tracking systems computes invertible transformations between a tracking system and a reference system, and applies an inverse of the transformation to measurements in the tracking system to estimate the locations of reference points in the reference system and to determine relative bias at the measured points.

Claims

1. A method, comprising:

tracking an object with features of known relative geometry in a tracking system; and

comparing a measured geometry of the features with the known geometry of the features to determine the relative position-dependent bias of the tracking system.

2. The method of claim 1, wherein tracking the object comprises:

calculating an invertible transformation between known locations of a first plurality of points in a reference coordinate system and measured locations of the first plurality of points in a tracking coordinate system; and

wherein comparing the measured geometry with the known geometry comprises;

applying an inverse of the invertible transformation to a measured location of a second point in the tracking coordinate system to obtain an estimated location of the second point in the reference coordinate system; and

generating a control signal representative of a difference between the estimated location of the second point in the reference coordinate system and a known location of the second point in the reference coordinate system, the difference corresponding to a relative position-dependent bias between the first plurality of points in the tracking coordinate system and the second point in the tracking coordinate system.

3. The method of claim 2, further comprising positioning a tracked surgical instrument in the reference coordinate system with the control signal to correct for the relative position-dependent bias in the tracking coordinate system.

4. The method of claim 2, further comprising positioning a tracked surgical target in the reference coordinate system with the control signal to correct for the relative position-dependent bias in the tracking coordinate system.

5. The method of claim 2, wherein the first plurality of points comprises a first plurality of fiducial markers and the second point comprises a second fiducial marker, wherein the first plurality of fiducial markers and the second fiducial marker are positioned at known locations on a calibration object.

6. The method of claim 5, wherein the calibration object defines the reference coordinate system.

7. The method of claim 5, wherein the reference coordinate system comprises an x-ray imaging system.

8. The method of claim 2, further comprising:

determining the known locations of the first plurality of points in the reference coordinate system and the known location of the second point in the reference coordinate system;

measuring the locations of the first plurality of points in the tracking coordinate system; and

measuring the location of the second point in the tracking coordinate system.

9. The method of claim 2, further comprising determining the relative position-dependent bias for a plurality of different second points over a region of interest in the tracking coordinate system to generate a map of relative position-dependent bias over the region of interest in the tracking coordinate system.

10. The method of claim 2, further comprising:

determining the relative position-dependent bias for a plurality of different second points bounding a region of interest in the tracking coordinate system; and

linearly interpolating the relative position-dependent bias between each of the plurality of different second points and a centroid of the first plurality of points.

11. An apparatus, comprising:

a tracking system to measure the locations of a first plurality of points in a tracking coordinate system and a second point in the tracking coordinate system, wherein the first plurality of points and the second point have known positions in a reference coordinate system; and

a processing device coupled with the tracking system, wherein the processing device is configured to calculate a rigid transformation between the measured locations of the first plurality of points in the tracking coordinate system and the known locations of the first plurality of points in the reference coordinate system,

wherein the processing device is further configured to apply an inverse of the rigid transformation to the measured location of the second point in the tracking coordinate system to obtain an estimate of the known location of the second point in the reference coordinate system, wherein a difference between the estimated location and the known location corresponds to a relative position-dependent bias between the first plurality of points in the tracking coordinate system and the second point in the tracking coordinate system.

12. The apparatus of claim 11, further comprising an instrument controller coupled with the processing device, wherein the instrument controller is configured to position a tracked instrument in the reference coordinate system to correct for the relative position-dependent bias in the tracking coordinate system.

13. The apparatus of claim 11, further comprising a positioning system coupled with the processing device to position a tracked target in the reference coordinate system to correct for the relative position-dependent bias in the tracking coordinate system.

14. The apparatus of claim 11, wherein the tracking system comprises an optical tracking system.

15. The apparatus of claim 11, wherein the tracking system comprises an infrared tracking system

16. The apparatus of claim 11, wherein the tracking system comprises a magnetic tracking system.

17. The apparatus of claim 11, wherein the processing device is further configures to determine a relative position-dependent bias for a plurality of different second points over a region of interest in the tracking coordinate system to generate a map of relative position-dependent bias over the region of interest in the tracking coordinate system.

18. The apparatus of claim 11, wherein the processing device is further configured to determine the relative position-dependent bias for a plurality of different second points bounding a region of interest in the tracking coordinate system and to linearly interpolate the relative position-dependent bias between each of the plurality of different second points and a centroid of the first plurality of points.

19. An apparatus, comprising

means for determining position-dependent bias in a tracking system;

and

means for removing the position-dependent bias within a region of interest in the tracking system.

20. The apparatus of claim 19, wherein the means for removing the position-dependent bias comprises:

means for mapping the position-dependent bias within the region of interest in the tracking system; and

means for correcting the position of one or more instrumentalities within the region of interest.